One of the primary life-dependencies of humans is continuous delivery of oxygen by the lungs and blood circulatory system to all tissues of the body in sufficient quantity to maintain aerobic metabolism; thus avoiding tissue injury from too little, or too much oxygen. To approximate this information, clinicians must mentally correlate measurements of breathing gas oxygen fraction, breathing rate, heart rate, cardiac output, blood hemoglobin level, arterial blood hemoglobin-oxygen saturation (“blood gas,” or SaO2), and pulse oximetry (SpO2), along with a subjective evaluation of arterial blood flow distribution. While each of these separate measurements are known to provide significant information, this currently available data, even with expert analysis, cannot provide the “bottom-line” tissue-level insight that has long been missing. Clinicians have long known that it is the tissue of vital organs, especially the brain, that is at risk of being injured; not the blood. The recently introduced Lumee™ sensor (Profusa), measures the oxygen level in tissue, but cannot indicate whether there is enough, or too much, oxygen. Also, the new sweat lactate sensor from Kenzen indicates when the skin is anaerobic, but cannot work when there is no sweat production and does not sense when too much oxygen is present. Without accurate, objective tissue-level information, the limitations of blood and tissue oxygen metrics, human sensory misperceptions and subjective clinician assessment errors in this critical part of medical care can inadvertently result in permanent vital organ tissue damage and possibly death. Thus, there is an unmet need in critical care medicine for an objective, reliable, and preferably non-invasive indicator of oxygen-related energy conversion metabolism at the tissue level.
Personal need and desire for basic physiologic information is also found in many areas of normal living, such as maintenance of general health and conditioning, obesity weight loss exercise, maintaining safety in recreational and workplace activities, and athletic training and performance. While “medical device-like” vital sign monitoring devices have recently been re-packaged into consumer-friendly “activity tracker” devices, the same limitations remain with respect to their delivery of physiologic information.